▼ Tungsten trioxide (WO3) films are important for various optical devices and
especially for electrochromic materials. Sputtered WO3 thin films were deposited on
conductive glass substrate (ITO/glass) by RF sputtering from a WO3 target(diameter
2âx 6 mm) in a reactive atmosphere of oxygen and argon flow ratio(0 to 1) mixture in
a total gas pressure of 10m Torr. The RF power was 100W operating at 13.56MHz.We
will improve the WO3 films by post-annealing in different atmosphere ambient.
In addition, to prepare treatment solution of growing WO3 films were dissolved
tungsten to aqueous which mixed hydrofluoric acid and nitric acid until it
supersaturate. This solution was then diluted to 0.02 M of tungsten ions with distilled
water. And we can get the treatment solution (WO3-HF aqueous). The WO3 thin films
have been deposited at 40 °C with the treatment solution (WO3-HF aqueous) which
full of W ions, the 0.1M boric acid (H3BO3) solution and added aluminium metal by
liquid phase deposition (LPD) technique. The deposition rate could be controlled to
45 nm/h.
In our experiment, the WO3 films morphology and thickness was characterized
by scanning electron microscopy(SEM), structure was characterized by X-ray
diffraction(XRD), chemical properties was characterized by X-ray photoelectron
spectroscopy(XPS) and Fourier transform infrared spectroscopy(FT-IR), optical
properties was characterized by spectrophotometer(MP-100M), and electrochromic
characterized by cyclic voltammetry(CHI627C).
In our results, it will be improved the optical and electrochromic properties of
sputtered-WO3 films by post-annealing in O2 ambient. we also have try a novel and
very simple process for the thin films of WO3 by the LPD process. Adherent and
conformal WO3 electrochromic films were prepared on ITO/glass from aqueous
fluoride solution.
Advisors/Committee Members: JengGong (chair), Tsu-Hsin Chang (chair), Ming-Kwei Lee (committee member), Kuo-Mei Chen (chair).

► In this study, we deposit titanium dioxide (TiO2) on the indium tin oxide (ITO/glass) substrate by a liquid phase deposition (LPD) method as a buffer…
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▼ In this study, we deposit titanium dioxide (TiO2) on the indium tin oxide (ITO/glass) substrate by a liquid phase deposition (LPD) method as a buffer layer and coat TiO¬2 particles on LPD-TiO2 films by spin-coating method as anode of dye-sensitize solar cell (DSSC). In order to adjust the optical absorption edge of titanium dioxide to the visible light, we co-dope fluorine and nitrogen into TiO2 by LPD method and Ammonium Fluoride (NH4F).
In our experiment, the morphology and thickness was characterized by scanning electron microscopy (SEM), structure was characterized by X-ray diffraction (XRD), chemical properties was characterized by electron spectroscope chemical analysis (ESCA), structural and spectral properties were characterized by ultraviolet-visible spectroscopy (UV-Vis) spectroscopy and current-voltage (I-V) characterization of solar cells was measured by B1500A.
In our results, we enhance the performance of TiO2 as a DSSC`s anode, the open circuit voltage can reach to 0.71 V, the short circuit current can reach to 5.14 mA, the conversion efficiency can reach to 1.91 % and the fill factor can reach to 52.5 %.
Advisors/Committee Members: JengGong (chair), Tsu-Hsin Chang (chair), Kuo-Mei Chen (chair), Ming-Kwei Lee (committee member).

▼ In this study, the reactive rf magnetron sputtering was used to deposit P- and N-type zinc oxide (ZnO) thin films, Zinc oxide (ZnO) has higher exiton bindingenergy (60 meV) and high band gap (~3.4 eV) that can provide efficient ultraviolet (UV) light at room temperature (RT). Intrinsic ZnO is thought to be N-type primarily because of donor defects such as zinc interstitials (Zni) and oxygen vacancies (VO). we want to prepared N-doped ZnO (ZnO:N) films, we used two method : Deposition Zn3N2 films by dc sputtering of Zn target in proportional Ar and N2 mixture. After deposition, it were thermally oxidized at difference temperatures to prepared N-doped ZnO (ZnO:N) films. And to make use of rf sputtering that ZnO target in proportional Ar and N2 mixture, to prepared N-doped ZnO (ZnO:N) films. The physical characteristics of ZnO thin films with different parameter were obtained by the analyses of field emission scanning electron microscopic (FE-SEM) and XRD. The electron spectroscopy for chemical analysis (ESCA) was used to analyze the chemical states of ZnO thin films. In optical properties, the photoluminescence spectrometer was used to measure the photoluminescence characteristics (PL).
Advisors/Committee Members: JengGong (chair), Kuo-Mei Chen (chair), Ming-Kwei Lee (committee member), Tsu-Hsin Chang (chair).

► In this study, we prepare the zinc oxide nanotip with aqueous solution deposited on ZnO nucleation layer. The thermal annealing with N2 ambiance at 300…
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▼ In this study, we prepare the zinc oxide nanotip with aqueous solution deposited on ZnO nucleation layer. The thermal annealing with N2 ambiance at 300 °C for 1 hr increase the UV emission and decrease the defects. We use ZnO nanotip as an anti-reflection layer because of surface roughness and optical interference. ZnO nanotip with rough surface decreases reflection, so we use ZnO nanotip as an anti-reflection layer, after grown ZnO nanotip on solar cell the efficiency of solar cell was enhancement.
The coordination modes were measured by Fourier-transform infrared spectrometer (FTIR). The physical properties were characterized by X-ray diffraction (XRD). The optical properties were measured by Micro-photoluminescence (Micro-PL). The morphology was observed by field emission scanning electron microscope (FE-SEM). The performance of the cells was measured by a semiconductor device analyzer. In our results, we grow the high performance of ZnO nanotip on solar cell to increase the efficiency. The short-circuit current increased from 42 to 51 mA, and the efficiency increased from 15.7 to 18.8 %.
Advisors/Committee Members: Tsu-hsin Chang (chair), JengGong (chair), Ming-kwei Lee (committee member), Chen-lin Ho (chair).

► Titanium oxide (TiO2) films have been actively investigated as many applications because of the mechanical and chemical durability, high refractive index and high transparency. In…
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▼ Titanium oxide (TiO2) films have been actively investigated as many applications because of the mechanical and chemical durability, high refractive index and high transparency. In catalytic and electrochemical applications, it has been utilized as a stable semiconductor electrode for the conversion of solar energy into chemical or electrical energy. Uniform TiO2 films were deposited on conductive glass substrate (ITO/glass) by liquid phase deposition (LPD) with the aqueous solutions of ammonium hexafluoro-titanate and boric acid.
Niobium oxide powder and Hydrofluoric acid which add deionized water were used to be Niobium doping solution. Undoped LPD-TiO2 has hydroxyl related defects and Li+ ions will be trapped to degrade the electrochromic durability. For niobium doping, the electrochromic characteristics were enhanced. Niobium doping in TiO2 can reduce hydroxyl related defects. The electrochromic durability was enhanced from 5Ã103 to 1Ã104 times. The transparency ratio was enhanced from 61 % to 70 % at the wavelength of 550 nm.
In our experiment, TiO2 films morphology and thickness was characterized by scanning electron microscopy (SEM), structure was characterized by X-ray diffraction (XRD) and surface roughness was measured by atomic force microscopy (AFM), chemical properties was characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR), optical properties was characterized by spectrophotometer (MP-100), and electrochromic characterized by cyclic voltammetry (CHI627C).
Advisors/Committee Members: Tsu-Hsin Chang (chair), Chen-Lin Ho (chair), JengGong (chair), Ming-Kwei Lee (committee member).

► In this study, the thin titanium oxide (TiO2) film deposited on InP substrate was prepared by atomic layer deposition (ALD), which was used as gate…
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▼ In this study, the thin titanium oxide (TiO2) film deposited on InP substrate was prepared by atomic layer deposition (ALD), which was used as gate oxide of InP Schottky barrier MOSFET. First, aluminum oxide (Al2O3) by ALD can be used as improvement in oxide of TiO2. Al2O3 of ALD has self-cleaning which can improve interface between oxide and substrate, the leakage current densities can reach 3.1 Ã 10-9 and 3.3 Ã 10-7 A/cm2. The Schottky barrier height(Î¦Bp) of Al/InP with (NH4)2S treatment is 0.968 eV, which is higher than that of Al/InP without (NH4)2S treatment (0.806eV). The (NH4)2S solution is a moderate etchant to reduce surface oxides on InP. Therefore, Schottky barrier will not be influenced by Fermi level pinning. The electrical characteristics of Schottky barrier MOSFET with TiO2 as gate oxide were measured in this report. The drain current is 1.73Î¼A. The drain current increases rapidly when drain voltage is over 1V, it indicates that breakdown field of TiO2 thin film is not high enough. Due to advantages of ALD-Al2O3, such as self-cleaning ability and high breakdown field, the TiO2/Al2O3 prepared by ALD structure was used to improve the problem mentioned above. The electrical characteristics are much improved compared with a single TiO2 film, and drain current can reach 1.37 Î¼A. The rapid increase of drain current with the increased drain voltage is not observed. The transconductance and mobility are 4.45 Ã 10-7 S/Î¼m and 202.3 mm2/V-s, respectively, and a good sub-threshold behavior is obtained. Compared with other researches, we can find that Schottky barrier in on-state is higher than that of silicide sample. It indicates the InP Schottky barrier MOSFET characteristics are limited by high Schottky barrier.
Advisors/Committee Members: Chen-Kin Ho (chair), Ming-Kwei Lee (committee member), JengGong (chair), Tsu-Hsin Chang (chair).

► Multiple gate devices have become the new trend, traditional bulk devices encounter many problems as the size continuously shrink due to short channel effect. Multiple…
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▼ Multiple gate devices have become the new trend, traditional bulk devices encounter many problems as the size continuously shrink due to short channel effect. Multiple gate devices have three dimensional wire structure and make devices more sides of gate. This improves the control ability of gate and effectively suppresses short channel effect. In this experiment, we observed different profiles of compound etching. Using the characteristics of etching to form the 3D-wire of multiple gate devices and then measure electronic characteristics of this structure.
Advisors/Committee Members: Ming-Kwei Lee (committee member), JengGong (chair), Chien-Jung Huang (chair), Ying-Chung Chen (chair), Ying-Chung Chen (committee member).

► Low cost and high efficiency are continuous interests for the fabrication of solar cells. I-III-VI compound semiconductor Cu(In,Ga)Se2 (CIGS) is the most important absorber material…
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▼ Low cost and high efficiency are continuous interests for the fabrication of solar cells. I-III-VI compound semiconductor Cu(In,Ga)Se2 (CIGS) is the most important absorber material in developing thin film solar cells. The band gap of CIGS varies from about 1.0 to 1.7 eV, which is within the maximum solar absorption region. This is very important for the optimum conversion efficiency. The extraordinarily high absorption coefficient from direct band gap leads to thinner thickness and lower fabrication cost for its use in thin film solar cells. In this experiment, we deposited CuInGa and Cu(In,Ga)Se2 alloy layers on soda-lime glasses by RF sputtering separately and then used selenization process to form Cu(In,Ga)Se2 thin films. We study the effects of selenized temperatures and processes on the qualities and characteristics of CIGS thin film.
Advisors/Committee Members: Min-Yan Ye (chair), Ying-Chung Chen (committee member), Ming-Kwei Lee (committee member), Chih-Feng Yen (chair), JengGong (chair).

► Due to the high electron mobility compared with Si, much attention has been focused on III-V compound semiconductors (gallium arsenide (GaAs), indium phosphide (InP), indium…
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▼ Due to the high electron mobility compared with Si, much attention has been focused on III-V compound semiconductors (gallium arsenide (GaAs), indium phosphide (InP), indium gallium arsenide (InGaAs)) high-speed devices. The high-k material TiO2 not only has high dielectric constant (k =35-100) but also has well lattice match with GaAs, InP and InGaAs substrate. Therefore, titanium oxide (TiO2) was chosen to be the gate oxide in this study, and aluminum oxide (Al2O3) has high bandgap (Eg~9eV) and self-cleaning capability, we use TiO2 and Al2O3 stack layers to decrease leakage currents and increase capacitance.
The major problem of III-V compound semiconductor is known to have poor native oxide on it leading to the Fermi level pinning at the interface of oxide and semiconductor. The C-V stretch-out phenomenon can be observed and the leakage current is high. Use atomic layer deposition (ALD) system to grow stack double layers ALD-TiO2 and ALD-Al2O3 films on III-V substrate by high-k of TiO2 and high bandgap and self-cleaning capability of Al2O3 to reduce only one layerâs defect.
The surface passivation of III-V with (NH4)2S treatment (S-III-V) could prevent it from oxidizing after cleaning and improve the interface properties of MOSFET. The leakage current of sulfur passivation can be improved. The leakage current densities are 7.31 x 10-7, 3.11 x 10-6 and 7.40 x 10-7 A/cm2 at Â±2.0MV/cm, respectively. The (NH4)2S is necessary to passivation III-V surface form S-thin film of fabrication of III-V devices.
Advisors/Committee Members: JengGong (chair), Min-Yen Yeh (chair), Chin-Feng Yen (chair), Ming Kwei Lee (committee member), Ying-Chung Chen (committee member).

► Silicon solar cell made from thin-film crystalline-silicon layers on glass substrates could lower the price of photovoltaic electricity substantially. For this reason, a considerable number…
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▼ Silicon solar cell made from thin-film crystalline-silicon layers on glass substrates could lower the price of photovoltaic electricity substantially. For this reason, a considerable number of methods have been proposed in the last decade to manufacture thin silicon foils which aim to replace the commonly used sawing technique. One of these methods âSLiM-Cutâ is based on peeling off a thin layer from a silicon substrate by means of the thermal stress induced by layers deposited on the silicon. Up to now, three different materials which are used to be deposited layers have been successfully employed in this technique: Nickel, Nickel/Chromium alloy and a Silver/Aluminium system. In this work we discuss the technology how to control the thickness of tearing-off films and the flatness of tearing-off films to make multiple tearing-off films from the same substrate.
Advisors/Committee Members: JengGong (chair), Min-Yan Ye (chair), Ying-Chung Chen (committee member), Ming-Kwei Lee (committee member), Chin-Feng Yen (chair).

► In this study, the characteristics of Nickel-doped LPD-TiO2 films on silicon substrate were investigated. In our experiment, we do some measurement about physical, chemical and…
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▼ In this study, the characteristics of Nickel-doped LPD-TiO2 films on silicon substrate were investigated. In our experiment, we do some measurement about physical, chemical and electrical properties for undoped and Nickel-doped LPD-TiO2 films and discussed with them. The TiO2 film thickness was characterized by field emission scanning electron microscopy ( FE-SEM ), structure was characterized by X-ray diffraction (XRD), chemical properties was characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and electrical properties was characterized by leakage current: current-voltage (B1500A) and dielectric constant: capacitance-voltage (4980A). For the electrical property improvements, we investigated the Ni-doped LPD-TiO2 films by the post-anneal treatments in nitrogen, oxygen and nitrous oxide ambient.
For nickel doping, the nickel chloride was used as the doping solution and the electrical characteristics were improved. After thermal annealing in nitrous oxide at 700 °C, the dielectric constant of polycrystalline titanium oxide film is 29 and can be improved to 94 with nickel doping.
Advisors/Committee Members: Kuo-mei Chen (chair), Yu-hao Yang (chair), JengGong (chair), Ming-kwei Lee (committee member), Chung-cheng Chang (chair).

► In recent years, even though the light output of GaN-based LED continues to increase, the brightness (~20 lm/W) is still low compared to conventional lighting…
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▼ In recent years, even though the light output of GaN-based LED continues to increase, the brightness (~20 lm/W) is still low compared to conventional lighting systems and it is necessary to further improve the light extraction of LEDs.
In this study, we utilize flip-chip technique, photoresist microlenses, reflectors and thermoelectric cooler to increase the light extraction of GaN MQW LED. Electroluminescence (EL) and power angular distribution are used to measure the light output intensity of LED. From temperature dependent current-voltage (I-V-T) characteristics, the charge carrier transport mechanisms at different biased regions are also investigated.
In the results, back emission of LED with SiO2/Al reflector has maximum light intensity ( 3.28Î¼W ) , which is higher than front emission one ( 2.73Î¼W ) in vertical emitting area ( at 90 angles). LED with P.R. microlenses (refractive index, n=1.62) on backside could improve the light extraction of LED (about 1.2 times) as well. The enhancement of light output is duo to the reduction of light absorption from the metal contact and Fresnelâs transmission losses at GaN (n=2.4)/air (n=1) interface.
Finally, we fabricate a high brightness LED with above light enhancement design. EL intensity of LED is increased about 1.25 times than conventional one. Therefore, we can manufacture a LEDs array with above designs to obtain high light output for future solid-state illumination.
Advisors/Committee Members: Ming-Kwei Lee (committee member), Tsu-Hsin Chang (chair), JengGong (chair), Wen-Tai Lin (chair).

▼ Recently, there has been increasing demands for high dielectric materials to replace SiO2 for high-density dynamic random access memories with ultralarge scale integration. TiO2 and BaTiO3 are very promising insulators for applications to DRAMs, as they exhibit higher dielectric constant.The growths of TiO2 and BaTiO3 thin films on (100) silicon are studied by MOCVD using Ti(i-OC3H7)4, Ba(DPM)2(tetraene)2 and N2O as precursors. The growth was performed in a cold wall horizontal system in the temperature range of 350~700â. The growth rates of TiO2 and BaTiO3 films are affected by the Ti flow rate, growth temperature and reactor pressure. The structures of TiO2 and BaTiO3 films are polycrystalline by X-ray diffraction examinations. The dielectric constant of as-grown TiO2 can reach 85 and BaTiO3 can reach 300 derived by C-V curves with the contact area 3.14Ã10-4 cm2. In addition, the influences of postannealing treatment under an O2 and N2 ambient with different annealing temperature and time on the structural and electrical properties of as-grown TiO2 films will be also studied.
However, TiO2 and BaTiO3 films have columnar structures acted the paths of leakage current. We use thermal annealing to reduce the leakage current. In the future, to enhance the dielectric constant and reduce the leakage current of the films is the goal in our study.
Advisors/Committee Members: JengGong (chair), Yeu-Hew Yang (chair), Dong-Sing Wuu (chair), Ming-Kwei Lee (committee member), Ray-Hua Horng (chair).

► ASTRACT Using an aqueous solution of ammonia hydroxide aqua, hydrosilicofluoric acid and boric acid, an oxynitride film can be deposited. The deposition rate and refractive…
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▼ ASTRACT
Using an aqueous solution of ammonia hydroxide aqua, hydrosilicofluoric acid and boric acid, an oxynitride film can be deposited. The deposition rate and refractive index increase with the mole concentration of ammonia hydroxide aqua. However, the refractive index decreases as the mole concentration of ammonia hydroxide aqua becomes too high. The leakage current density as a function of mole concentration of ammonia hydroxide aqua was studied. The best experimental condition is found that incorporating ammonia hydroxide aqua of 0.8M will get good results.
The SIMS depth profiles shows nitrogen and hydrogen concentration accumulate at SiON/Si interface. A deposition model is proposed and LPD-SiON can be suggested that it is a combination of N-less LPD-SiON film and N-rich accumulated layer at the interface. The best characteristics of LPD-SiON film are in the range of 110Å-thick to 210Å-thick. When the thickness scales down to 110Å, all the properties become poor.
Photo-LPD-SiON process is proposed as a reference of Photo-LPD-SiO2. By mercury lamp illumination, the performances of J-E relationship and C-V characteristic become better. Nitrogen atomic concentration can increase by photo-enhancement checked by analysis of SIMS depth profile and FTIR spectrum.
A novel technique of LPD process with applying a bias during the growth is proposed and it is called Bias-LPD-SiON. A model of Bias-LPD-SiON deposition mechanism is also proposed. On the negative bias substrate, high nitrogen atomic concentration can be attained. The J-E characteristic at positive bias of 0.1V and negative bias in a range of 0.1V to 1V are better than traditional LPD-SiON film. Then, the deposition rate of positive bias and negative bias LPD-SiON films at 0.1V can reach 32Å/min and 26Å/min, respectively. Therefore, high quality and high deposition rate can be prepared by Bias-LPD-SiON.
Advisors/Committee Members: Ming-Kwei Lee (committee member), Yeu-Hew Yang (chair), Ray-Hua Horng (chair), JengGong (chair), Don-Sing Wuu (chair).

► When the size of display panel increased, the RC delay of TFTs became serious.In order to solve this problem, it is necessary to incorporate a…
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▼ When the size of display panel increased, the RC delay of TFTs became serious.In order to solve this problem, it is necessary to incorporate a high dielectric (high-k) material used as the gate oxide can increase the gate oxide capacitance Co, which can induce a higher drain current and higher aperture ratio.
In this study, titanium silicon oxide films were grown on amorphous silicon and poly-crystal silicon by liquid phase deposition, the addition of NH4OH in the growth solution can control the PH value and prevent the amorphous and poly-crystalline silicon over etching by HF.
The physical and chemical properties of titanium silicon oxide film by means of several measuring instruments, including Fourier transform infrared spectrometer (FTIR), and X-Ray diffractometer (XRD). An Al/titanium silicon oxide/a-Si or poly-Si/Si metal-oxide-semiconductor (MOS) capacitor structure was used for the electrical measurements. After oxygen and nitrogen annealing, the leakage current is improved due to the reduction of the oxygen vacancy of titanium silicon oxide film. However, the electrical characteristics can be further improved by the postmetallization annealing treatment especially under the negative electric field.
Post-metallization annealing (PMA) is to use the reaction between the aluminum contact and hydroxyl groups existed on oxide surface to form active hydrogen and diffuse through the oxide to passivate the oxide traps. Therefore, titanium silicon oxide
film which treated by PMA with higher dielectric constant and lower leakage current can be obtained.
Advisors/Committee Members: Tsu-Hsin Chang (chair), Yu-Hao Yang (chair), Chung-Cheng Chang (chair), Ming-Kwei Lee (committee member), JengGong (chair).

► For MOCVD-TiO2/Si MOS structure, oxygen vacancy and grain boundary are the main defects of polycrystalline TiO2 films. They are the main mechanisms for the leakage…
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▼ For MOCVD-TiO2/Si MOS structure, oxygen vacancy and grain boundary are the main defects of polycrystalline TiO2 films. They are the main mechanisms for the leakage current. In order to improve the problems, oxygen annealing treatment is often used for filling oxygen vacancies. The electrical characteristics of as-grown MOCVD-TiO2 films can be improved. However, it is from the lattice mismatch between the TiO2 film and Si substrate. In order to release the stress, the TiO2 film will produce a lot of defects and degrade its stoichiometry. Besides, the thermal ionic emission is due to lower conduction band offset between TiO2/Si than that of SiO2/Si. These problems need further improvement.
In order to solve the above mentioned problems, fluorinated liquid phase deposition (LPD) SiO2 deposited upon polycrystalline MOCVD-TiO2/Si. Higher barrier height (Eg = 9 eV) of fluorinated LPD-SiO2 could avoid the thermal ionic emission from lower conduction band offset of TiO2/Si. Moreover, the LPD-SiO2 film can provide fluorine (F-) from the hydrofluosilicic acid (H2SiF6) aqueous solution. Fluorine could passivate grain boundaries of poly-crystalline MOCVD-TiO2 films and interface state density (Dit) of the MOCVD-TiO2/Si interface. The main leakage current of polycrystalline MOCVD-TiO2 films could be .effective to reduce. Furthermore, nitrogen (N2) annealing was used to enhance fluorine passivation of LPD-SiO2/O2-annealed MOCVD-TiO2 films. Therefore, it can be expected that higher dielectric constant and lower leakage current density will be obtained from
LPD-SiO2/O2-annealed MOCVD-TiO2/Si MOS structure. Therefore, MOSFET with fluorinated MOCVD-TiO2 gate oxide can have lower off state leakage current, smaller subthreshold swing, higher transconductance, and higher field effect mobility.
On the other hand, LPD-SiO2/MOCVD-TiO2 film on (NH4)2Sx-treated GaAs not only can lower leakage current but can lower interface state density. The leakage current densities are 2.3Ã10-7 A/cm2 and 3.6Ã10-7A/cm2 under positive and negative electric fields at 10V, respectively. The lowest interface state density is 4.7Ã1011 cm-2eV-1 in the band gap. Moreover, the dielectric constant can reach 62. Therefore, LPD-SiO2/MOCVD-TiO2/(NH4)2Sx-treated GaAs structure is a high dielectric constant and low leakage current film. This structure has high potential for the further development of GaAs MOSFETs.
Advisors/Committee Members: Yu-Hao Yang (chair), Wen-Tai Lin (chair), JengGong (chair), Ming-Kwei Lee (committee member), Ikai Lo (chair).

► The purpose of this study is using titanium dioxide (TiO2) as gate oxide on thin film transistor (TFT) and discussed with their physical, chemical and…
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▼ The purpose of this study is using titanium dioxide (TiO2) as gate oxide on thin film transistor (TFT) and discussed with their physical, chemical and electrical properties. Amorphous silicon (a-Si) and polycrystalline silicon (poly-Si) are used as substrates. The metal-organic chemical vapor deposition (MOCVD) and the liquid phase deposition (LPD) are used as the TiO2 growth methods. About the LPD growth method, ammonium hexafluoro-titanate ((NH4)2TiF6) and hexafluorotitanic acid (H2TiF6) are used as Ti sources. We are interested in two parts: (1) the growth mechanisms, physics properties, chemical properties and electrical properties of MOS structure; (2) the fabrication processes and electrical properties of devices.
In the first part, we discuss the thin films characteristics on a-Si and poly-Si substrates. For the MOCVD growth method, the MOCVD-TiO2 film tends to form the poly structure. Poly structure has a higher dielectric constant, however, higher traps and dangling bonds also exist at the grain boundaries. Thus, poly structure of TiO2 film has a higher leakage current. For the LPD growth method, the film tends to form the amorphous structure. Amorphous structure has lower leakage current but also has lower dielectric constant. The film that grown from the (NH)2TiF6 source is called LPD-TiO2 film. The film that grown from the (NH)2TiF6 source is called LPD-TixSi(1-x)Oy film. Both films are incorporated with OH and F ions during the growth, the OH and F ions can be outgassed during the low temperature annealing process. In addition, appropriate F ions in the film can passivate the traps and dangling bonds. The low temperature treatments in N2 or O2 ambient and post-metallization annealing (PMA) are adopted to improve the film characteristics. On the other hand, the substrate is not a prefect structure (not a single structure). Thus the film may be influenced by substrate during the annealing treatment.
In the second part, the electrical properties of TFT devices were discussed under the coplanar structure. There are several differences of the operation principle in TFT and MOSFET. A-Si and poly-Si are the un-doped substrates with many traps in the bulk. The channel should be occurred through the full depletion mode. The full depletion region is the substrate that under the gate electrode. Thus, the key point is kept the suitable thickness. Too thick, the channel can not appear. Too thin, the substrate may be over-etched. For ion implantation, due to the thinner active layer, the ion implantation energy should be lowed. In addition, the activation temperature and activation time should be adjusted suitable. We have fabricated the TFT devices with the MOCVD-TiO2 as gate oxide on poly-Si substrate. From the I-V characteristics, the Kink effect can be observed. However, the Ion/Ioff ratio is still low. We must further study how to increase the Ion/Ioff ratio.
Advisors/Committee Members: JengGong (chair), Kuo-Mei Chen (chair), Ming-Kwei Lee (committee member), Chung-Cheng Chang (chair), Jen-Sue Chen (chair), Tsu-Hsin Chang (chair).

► Liquid Phase Deposited (LPD) TiO2 film technology and the characterization of films were described in detail in this thesis. The LPD-TiO2 film can be utilized…
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▼ Liquid Phase Deposited (LPD) TiO2 film technology and the characterization of films were described in detail in this thesis. The LPD-TiO2 film can be utilized in electrochromic, photocatalyst and gas sensor devices. The optimum parameters for deposition of LPD-TiO2 were studied.
First of all, we study the deposition properties and deposition parameter of LPD-TiO2 film. The effect of heating treatment on LPD-TiO2 film was investigated in this thesis. The as-deposited LPD-TiO2 film is amorphous and the TiO2 anatase phase can be obtained by annealing at 400 â. The rutile phase can be observed at the annealing temperature of 900 â. After annealing, the crystalling characteristic of LPD-TiO2 film can be improved and its refractive index can reach 2.46 annealed in O2 ambience. Its dielectric constant can be as high as 17 at annealing temperature of 700 â in O2 ambience.
LPD-TiO2 film can deposit on GaAs substrate successfully. The GaAs was etched by the treatment solution during deposition. Therefore, Ga and As are contained in the LPD film. The C-V characterization can be improved at annealing 400 â. But the leakage current increases with higher annealing temperature.
The electrochromic (EC) phenomena of TiO2 have been first reported by Inoue et al., where the films are prepared by hydrolysis of titanium tetraoxide. The film shows cathodic coloration and turns dark blue. The LPD-TiO2 film was deposited at 40 â with (NH4)2TiF6 in the process of 0.1 M and 0.2 M boric acid. The films were transparent in the visible range and can be colored in a 1M LiClO4 + propylene carbonate solution. The deposition rate can be controlled quite well at 43 nm/hours. The 270 nm thickness LPD-TiO2 film gives the best electrochromic characteristic.
In order to further strength the feasibility and enlarge the application of LPD-TiO2 film. The characterizations of Nb, Au and Pt doped LPD-TiO2 film were investigated. The concentrations of Nb and Au in the film can be controlled by adjusting the concentrations of Nb and Au source solution added into the treatment solution, respectively. The Nb, Au and Pt species in the LPD-TiO2 film are Nb2O5, metallic Au and Pt(OH)x, respectively. The crystallite size of metal-doped LPD-TiO2 film is smaller than that of pure LPD-TiO2 film.
The photocalytic activities of undoped and Nb-doped LPD-TiO2 film were investigated. The photocatalytic activity of Nb-doped LPD-TiO2 film is about four times higher than that of pure LPD-TiO2 film.
The gas sensing properties of undoped and Nb, Au and Pt-doped LPD-TiO2 films were investigated for oxygen detection sensitivity. Experimental results show that the Nb-doped LPD-TiO2 film displays the highest in oxygen detection, and the Nb-doped LPD-TiO2 film has also a shorter response time.
Advisors/Committee Members: JengGong (chair), Bae-heng Tseng (chair), Kuo-mei Chen (chair), Mau-phon Houng (chair), Wen-tai Lin (chair), Yeong-her Wang (chair), Ming-kwei Lee (committee member).

► High quality ammonium oxofluorotitanate discoid crystal is successfully grown on glass with an aqueous solution of ammonium hexafluorotitanate and boric acid at the molar ratio…
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▼ High quality ammonium oxofluorotitanate discoid crystal is successfully grown on glass with an aqueous solution of ammonium hexafluorotitanate and boric acid at the molar ratio of 0.6. The concentration of hydrofluoric acid is less on the glass substrate surface and enhances the ammonium oxofluorotitanate nucleation growth. The growth rate is much higher than that grown on dioctadecyldimethylammonium. From the examinations of X-ray diffraction and high-resolution transmission electron microscopy, the crystal shows high crystalline quality and uniformity. Each titanium oxide octahedral is linked with fluorine and nitrogen atoms. Therefore, ammonium oxofluorotitanate has high potential to be thermally decomposed into high crystalline fluorine and nitrogen co-doped titanium oxide.
A simple process for the preparation of nanocrystalline anatase phase titanium oxide converted from ammonium oxofluorotitanate by thermal treatment was developed. The nanocrystalline anatase phase titanium oxide shows a large bandgap reduction due to the co-doping of high concentrations of fluorine and nitrogen. Due to the excellent nanocrystalline quality and the co-doping of higher concentrations of fluorine and nitrogen at the thermal treatment temperature of 800 OC, it is 1.3 times the photocatalytic activities of P-25 due to the visble region usage of Hg lamp light source. The 11.2 times the visible photocatalytic activities of P-25 using blue light-emitting diode as the light source is obtained from thermal treatment temperature of 600 OC. There is one to one correspondence between carrier lifetime and photocatalytic activity. As a result, a highly reactive and visible-light-driven photocatalysis is achieved.
The heterostructure of zinc selenide/titanium oxide and zinc sulfide/titanium oxide were prepared by metal-organic chemical vapor deposition on the above-prepared titanium oxide. The energy bandgap of zinc sulfide is much larger than that of titanium oxide and can act as a window for titanium oxide. It would not hinder titanium oxide absorption and preserve the role of fluorine and nitrogen co-doping. The energy bandgap of zinc selenide is near the maximum intensity of solar spectrum and acts as a sensitizer of titanium oxide. The lifetime of electron and hole pairs of heterostructure are about 240 and 207 nsec, which are longer than 65 nsec of titanium oxide prepared at 800 °C thermal treatment. Their photocatalytic activities are further improved to 2.0 and 1.5 times higher than that of commercial P-25. The photocatalysis of titanium oxide is very sensitive to the surface states. Titanium oxide surface defects can act as trapping sites for photo-induced holes and facilitate the separation of photo-induced carriers. Zinc selenide and zinc sulfide can passivate the surface well. It may say that titanium oxide surface defects removal has a negative impact.
The density, height, diameter, PL wavelength and intensity of zinc selenide self-assembled quantum dots grown on zinc sulfide/gallium arsenide with the zinc sulfide thickness from…
Advisors/Committee Members: Tsu-Hsin Chang (chair), Chung-Cheng Chang (chair), Jen-Sue Chen (chair), Kuo-Mei Chen (chair), Yu-Hao Yang (chair), Ming-Kwei Lee (committee member), Yeong-Her Wang (chair), JengGong (chair).